1. Field of the Invention
The present invention relates to a piezoelectric element configured of a lower electrode, piezoelectric layers and upper electrodes as well as a method of manufacturing the piezoelectric element. Specifically, the present invention relates to a liquid-jet head which ejects droplets from nozzle orifices, and a method of manufacturing the liquid-jet head as well as a piezoelectric element used for a liquid-jet apparatus.
2. Description of the Prior Art
An inkjet recording head with the following configuration has been put into practical use. In accordance with the configuration, a part of pressure generating chambers communicating with nozzle orifices from which ink droplets are ejected is constructed with a vibration plate. The vibration plate is deformed by piezoelectric elements, and thus ink in each of the pressure generating chambers is pressurized. Accordingly, ink droplets are ejected from each of the nozzle orifices.
An inkjet recording head which is constructed, for example, in the following manner is among such inkjet recording heads. An even layer made of a piezoelectric material is formed on the entire surface of the vibration plate by use of a film-forming technique. Then, this layer made of the piezoelectric material is cut into shapes corresponding to the pressure generating chambers by the lithography method. Thereby, the piezoelectric elements are formed in order that the piezoelectric elements respectively in the pressure generating chambers can be independent from one anther.
A piezoelectric element having a piezoelectric layer which is formed in the following manner has been proposed as such a piezoelectric element used for the inkjet recording heads. First, an iridium layer made of iridium (Ir), a platinum layer made of platinum (Pr) and an iridium layer made of iridium (Ir) are sequentially laminated over one another by use of an adhesion layer including titanium (Ti) provided on top of the zirconia (ZrO2), and thus the lower electrode film is formed. Then, the piezoelectric layer is formed on top of this lower electrode film by the sol-gel method. (See pp. 9-10 and FIG. 3 of Japanese Patent Official Gazette No. 3517876, for example)
Such a piezoelectric layer is formed with a predetermined thickness by means of repeatedly laminating a plurality of piezoelectric films over one another, each of piezoelectric films being made of a thin film. However, the lower electrode film is also heated at the same time as the piezoelectric films are heated while the piezoelectric films are being formed. As a result, iridium is thermally oxidized, and thus an iridium oxide film made of the iridium oxide (IrO2) is formed, in a part of the lower electrode, the part being closest to the piezoelectric films. When such an iridium oxide layer is formed, it is likely that a stress may be concentrated between the iridium oxide layer and a mixed film made of an alloy of the iridium, the platinum and the titanium, and that an inter-layer detachment may occur in the lower electrode film. Such an inter-layer detachment in the lower electrode film obviously appears in a case where a plurality of laminated piezoelectric films are formed.
It should be noted that, such problems are not limited to liquid-jet heads represented by inkjet recording heads and methods of manufacturing the liquid-jet heads. The problems are similarly present in piezoelectric elements and methods of manufacturing the piezoelectric elements.